1. Field of the Invention
The present invention relates to a display device, and, more particularly, to an in-plane-switching mode liquid crystal display device using a ferroelectric liquid crystal material and a method of fabricating the same.
2. Discussion of the Related Art
In general, a liquid crystal display (LCD) device controls an electric field applied to a liquid crystal cell. The controlling of the electric field modulates light incident to the liquid crystal cell, thereby displaying a picture. The liquid crystal display devices may employ a vertical electric field method and a horizontal electric field method to drive the liquid crystal cell.
In the vertical electric field method, a pixel electrode and a common electrode are formed on an upper substrate and a lower substrate, respectively. Thus, the pixel and common electrodes are vertically opposite to each other, and an electric field is generated vertically across a liquid crystal cell by a voltage difference applied between the pixel and common electrodes. For example, a twisted nematic (TN) mode LCD device generally uses the vertical electric field method. The twisted nematic mode LCD device has a relatively wide aperture ratio. However, since the liquid crystal molecules have different refractive indices, a display picture varies for an observer depending on a viewing angle. Thus, there is a disadvantage that the realization of wide viewing angle is difficult.
Further, in-plane-switching (IPS) mode LCD devices generally use the horizontal electric field method. In the horizontal electric field method, an electric field is generated between the electrodes formed on the same substrate to drive the liquid crystal cell.
FIG. 1 is a schematic cross-sectional view of an in-plane-switching mode liquid crystal display device according to the related art. In FIG. 1, a liquid crystal display device includes an upper glass substrate 12 and a lower glass substrate 18 with a liquid crystal layer having liquid crystal molecules 14 formed therebetween. A polarizer 11 and an alignment layer 13 are respectively formed on an upper surface and a lower surface of the upper substrate 12. In addition, an alignment film 17 and a polarizer 19 are respectively formed on an upper surface and a lower surface of the lower substrate 18. In particular, the axes of the polarizers 11 and 19 cross each other.
Further, a common electrode 15 and a pixel electrode 16 are formed on the alignment film 17 on the lower substrate 18. In particular, an electric field 20 is generated along a horizontal direction by a voltage difference applied between the common electrode 15 and the pixel electrode 16. As a result, the liquid crystal molecules 14 are rotated by the electric field 20, thereby modulating a polarization component of light transmitting through the liquid crystal layer. For instance, if the polarization component of light transmitting through the liquid crystal layer is changed by 90 degrees, then light passes through the upper polarizer 11. On the other hand, if the polarization component of light does not change, then light cannot pass thorough the upper polarizer 11.
The IPS mode liquid crystal display device according to the related art has a wide viewing angle since a refractive index change of the liquid crystal molecules 14 is not large. However, the electric field applied to the liquid crystal molecules 14 is done with the opaque common and pixel electrodes 15 and 16 on the lower substrate 18. In particular, because a light switching is not made on the common and pixel electrodes 15 and 16, the electric field applied to the liquid crystal molecules 14 is bent. Thus, the IPS mode liquid crystal display device according to the related art has a disadvantage of having a low aperture ratio.